Lubricating oils comprising low saturate basestock

ABSTRACT

Multigrade lubricating oils for use in lubricating internal combustion engines, using basestocks with low levels (&lt;75 mass %) of saturated hydrocarbons, comprise less than 3 mass % of ashless dispersant derived from a polymer of number average molecular weight (Mn) of not greater than 5000, and a viscosity modifier package to give the desired viscometrics comprising at least one multifunctional viscosity modifier. These oils meet stringent engine performance requirements and specifically give adequate varnish inhibition without very high treat levels of dispersants and/or use of specific detergent systems so avoiding problems of oxidation stability, compatibility and engine performance debits.

This invention relates to multigrade lubricating oils for use inlubricating internal combustion engines, that contain basestocks withlow levels of saturated hydrocarbons, and specifically to such oilswhich also comprise a multifunctional viscosity modifier.

Multigrade lubricating oils typically are identified by designationssuch as SAE 10W-30, 5W-30 etc. The first number in the multigradedesignation is associated with a maximum low temperature (e.g.,-20° C.)viscosity requirement for that multigrade oil as measured typically by acold cranking simulator (CCS) under high shear rates (ASTM D5293, whichis a revision of ASTM D2602), while the second number in the multigradedesignation is associated with a high temperature viscosity requirementusually measured in terms of the kinematic viscosity (kV) at 100° C.(ASTM D445). Thus, each particular multigrade oil must simultaneouslymeet both strict low and high temperature viscosity requirements, sete.g. by SAE specifications such as SAE J300, in order to qualify for agiven multigrade oil designation.

The high temperature viscosity requirement is intended to prevent theoil from thinning out too much during engine operation which can lead toexcessive wear and oil consumption. The maximum low temperatureviscosity requirement is intended to facilitate engine starting in coldweather and to ensure pumpability, i.e., the cold oil should readilyflow to the oil pump, otherwise the engine can be damaged due toinsufficient lubrication.

The viscosity characteristic of a basestock on which a lubricating oilis based is typically expressed by the neutral number of the oil (e.g.,S150N) with a higher neutral number being associated with a higherviscosity at a given temperature. Blending basestocks is one way ofmodifying the viscosity properties of the resulting lubricating oil.Unfortunately, merely blending basestocks of different viscositycharacteristics may not enable the formulator to meet the low and hightemperature viscosity requirements of some multigrade oils. Theformulator's primary tool for achieving this goal is an additiveconventionally referred to as a viscosity modifier (VM) or viscosityindex improver (V.I. improver).

A monofunctional VM is conventionally an oil-soluble long chain polymer.A multifunctional VM (or alternately MFVM) is an oil soluble polymerwhich has been chemically modified e.g., functionalized and derivatized,to impart dispersancy as well as viscosity modification.

The basestocks which are typically used in lubricating oils may besynthetic or natural oils. Mineral oils contain various amounts ofsaturated hydrocarbons, such as straight or branched chain paraffins andnaphthenes, and unsaturated hydrocarbons particularly aromatichydrocarbons. Lubricating oils have traditionally used basestockscontaining high levels of saturated hydrocarbon--also referred to ashigh saturate basestocks--since aromatic hydrocarbons give rise todifficulties in formulating for adequate performance in internalcombustion engines. This has been known for some time, being discussed,for example, in "Lubricants for Fluid Film and Hertzian ContactConditions", T. I. Fowle, Proc. Instn. Mech. Engrs. 1967-8, Vol 182, Pt3A, pages 568-576, especially pages 568/9 and 571/2. More recently,"Chemistry and Technology of Lubricants", edited by R. M. Mortier and S.T. Orszulik, Blackie Academic and Professional, 1992, in chapter 1,"Base oils from Petroleum" R. J. Prince, pages 1-31, discusses theinstability of aromatic components to oxidation which is still perceivedas a problem. "Compositional Analysis of Re-refined and Non-ConventionalLubricant Base Oils: Correlations to Sequence VE and IIIE GasolineEngine Tests", Stipanovic et aL, SAE Technical Paper Series, 941978,Oct. 17-20 1994 provides a statistical analysis in those engine testswhich indicates a strong negative impact of various aromatic hydrocarbontypes. Among other consequences it is generally accepted that there is atendency for unsaturated components and particularly aromatic componentsof basestocks to contribute to the formation of baked-on deposits inengines, generally referred to as "varnish".

As discussed in the literature identified above, special and expensivefinishing treatments are required to remove aromatics from basestocksand so increase the level of saturates. Increasingly there is a need forlubricating oils for internal combustion engines which are capable ofutilising basestocks with low levels of saturates. In order to meetstringent engine performance requirements and specifically to giveadequate varnish inhibition to those oils with conventional types ofadditive formulations it has proved necessary to use very high treatlevels of dispersants and/or to use specific detergent systems. This iseconomically undesirable and also give rise to further problem withinthe oil formulation, as those high levels of additives can bring theirown problems of oxidation stability, compatibility and engineperformance debits.

This invention relates to multigrade lubricating oils which utilise lowsaturate basestocks and provide adequate varnish performance withoutrequiring high levels of dispersant and/or detergent additives.

Thus, in one aspect the invention provides a multigrade lubricating oilfor an internal combustion engine which comprises:

a. a basestock of lubricating oil viscosity having less than 75 mass %of saturated hydrocarbons;

b. less than 3 mass % of ashless dispersant derived from a polymer ofnumber average molecular weight (Mn) of not greater than 5000; and

c. viscosity modifier to give the desired viscometrics, which comprisesat least one multifunctional viscosity modifier.

DETAILED DESCRIPTION A. Basestock

As indicated above conventional lubricating oils are prepared usingbasestocks which have relatively high levels of saturates and thus lowlevels of unsaturated and specifically aromatic hydrocarbons. Mineralbasestocks are typically subjected to hydrogen treatments such ashydrocracking or hydroisomerisation in order to give greater paraffiniccontent and lower aromatic content. The basestock used in thelubricating oil of the invention does not require such treatments andmay use lower grade basestocks previously regarded as unsuitable forsuch applications. Such basestocks for use in the invention aretypically mineral oils which have not been subjected to severetreatments to raise the saturates level, but the invention may employany of the available synthetic or natural oils, re-refined oils andmixtures of such oils, provided the overall saturates level of thebasestock or basestock mixture is less than 75 mass %, preferably lessthan 70 mass %, and may even use basestocks of less than 65 mass %saturates. Such basestocks may contain at least 20%, preferably at least30 mass % of aromatic compounds and may even contain in excess of 35mass % of aromatic compounds.

Additives used in formulating lubricating oils often contain diluentoil; this diluent oil introduced with additives is not included withinthe term "basestock" as that term is used herein, which is confined tothe oil used to dilute the additives to form the finished oil.

The lubricating oil basestock conveniently has a viscosity of from 2.5to 12 mm² /s, and preferably from 2.5 to 9 mm² /s, at 100° C. Examplesof commercially available basestocks of low saturates content which maybe employed in the invention are ESN 600 (typically 69.9 mass %saturates; 30.1 mass % aromatics) available from Esso Petroleum Co.Ltd., Agip 450 (typically 64.7 mass % saturates; 35.3 mass % aromatics)available from Agip Petroli and BP 500ME (typically 61.9 mass %saturates; 38.1 mass % aromatics) available from B.P. pic. Such lowsaturate basestocks may be used alone or in combination with otherbasestocks, which may also have low saturates content or have relativelyhigher saturate content, provided that the saturate content of thecombined basestock as that term is used herein is less than 75 mass % ofthe total basestock.

B. Ashless Dispersant

The ashless dispersant comprises an oil soluble polymeric hydrocarbonbackbone having functional groups that are capable of associating withparticles to be dispersed. Typically, the dispersants comprise amine,alcohol, amide, or ester polar moieties attached to the polymer backboneoften via a bridging group. The ashless dispersant may be, for example,selected from oil soluble salts, esters, amino-esters, amides, imides,and oxazolines of long chain hydrocarbon substituted mono anddicarboxylic acids or their anhydrides- thiocarboxylate derivatives oflong chain hydrocarbons; long chain aliphatic hydrocarbons having apolyamine attached directly thereto, and Mannich condensation productsformed by condensing a long chain substituted phenol with formaldehydeand polyalkylene polyamine.

The oil soluble polymeric hydrocarbon backbone is typically an olefinpolymer, especially polymers comprising a major molar amount (i.e.greater .ia 50 mole %) of a C₂ to C₁₈ olefin (e.g., ethylene, propylene,butylene, isobutylene, pentene, octene-1, styrene), and typically a C₂to C₅ olefin. The oil soluble pentene, octene-1, styrene), and typicallya C₂ to C₅ olefin. The oil soluble polymeric hydrocarbon backbone may bea homopolymer (e.g. polypropylene or polyisobutylene) or a copolymer oftwo or more of such olefins (e.g. copolymers of ethylene and analphaolefin such as propylene and butylene or copolymers of twodifferent alpha-olefins). Other copolymers include those in which aminor molar amount of the copolymer monomers, e.g., 1 to 10 mole %, is aC₃ to C₂₂ non-conjugated diolefin (e.g., a copolymer of isobutylene andbutadiene, or a copolymer of ethylene, propylene and 1,4-hexadiene or5-ethylidene-2-norbornene).

One preferred class of olefin polymers is polybutenes and specificallypolyisobutenes (PIB) or poly-n-butenes, such as may be prepared bypolymerization of a C₄ refinery stream.

Another preferred class of olefin polymers is ethylene alpha-olefin(EAO) copolymers or alpha-olefin homo- and copolymers having in eachcase a high degree (e.g.>30%) of terminal vinylidene unsaturation. Thatis, the polymer has the structure: P-HCR=CH₂ wherein P is the polymerchain and R is a C₁ -C₁₈ alkyl group, typically methyl or ethyl.Preferably the polymers have at least 50% of the polymer chains withterminal vinylidene unsaturation. EAO copolymers of this type preferablycontain 1 to 50 mass % ethylene, and more preferably 5 to 45 mass %ethylene. Such polymers may contain more than one alpha-olefin and maycontain one or more C₃ to C₂₂ diolefins. Also usable are mixtures ofEAO's of low ethylene content with EAO's of high ethylene content. TheEAO's may also be mixed or blended with PIB's of various Mn's orcomponents derived from these may be mixed or blended. Atactic propyleneoligomer typically having Mn of from 700 to 500 may also be used, asdescribed in EP-A490454.

Suitable olefin polymers and copolymers, such as polyisobutenes, may beprepared by cationic polymerization of hydrocarbon feedstreams, usuallyC₃ -C₅, in the presence of a strong Lewis acid catalyst and a reactionpromoter, usually an organoaluminum such as HCI or ethylaluminumdichloride. Tubular or stirred reactors may be used. Suchpolymerizations and catalysts are described, e.g., in U.S. Pat. Nos.4,935,576 and 4,952,739. Fixed bed catalyst systems may also be used asin U.S. Pat. No. 4,982,045 and UK-A 2,001,662. Most commonly,polyisobutylene polymers are derived from Raffinate I refineryfeedstreams. Conventional Ziegier-Natta polymerization may also beemployed to provide olefin polymers suitable for use to preparedispersants and other additives.

The preferred EAO polymers may be prepared by polymerizing theappropriate monomers in the presence of a catalyst system comprising atleast one metallocene (e.g. a cyclopentadienyl-transition metalcompound) and preferably an activator, e.g. an alumoxane compound. Themetallocenes may be formed with one, two, or more cyclopentadienylgroups, which are substituted or unsubstituted. The metallocene may alsocontain a further displaceable ligand, preferably displaced by acocatalyst--a leaving group--that is usually selected from a widevariety of hydrocarbyl groups and halogens. Optionally there is a bridgebetween the cyclopentadienyl groups and/or leaving group and/ortransition metal, which may comprise one or more of a carbon, germanium,silicon, phosphorus or nitrogen atom-containing radical. The transitionmetal may be a Group IV, V or VI transition metal. Such polymerizationsand catalysts are described, for example, in U.S. Pat, Nos. 4,871,705,4,937,299, 5,017,714, 5,120,867, 4,665,208, 5,153,157, 5,198,401,5,241,025, 5,057,475, 5,096,867, 5,055,438, 5,227,440, 5,064,802;EP-A-129368, 520732, 277003, 277004, 420436; WO91/04257, 93/08221,93/08199 and 94/13715.

The oil soluble polymeric hydrocarbon backbone of the ashlessdispersant, as that term is used herein, has a number average molecularweight (Mn) of not greater than 5,000. The Mn of the backbone ispreferably within the range of 500 to 5,000, more preferably 700 to5,000 where the use of the backbone is to prepare a component having theprimary function of dispersancy. Hetero polymers such as polyepoxidesare also usable to prepare components. Both relatively low molecularweight (Mn 500 to 1500) and relatively high molecular weight (Mn 1500 to5,000) polymers are useful to make dispersants. Particularly usefulolefin polymers for use in dispersants have Mn within the range of from1500 to 3000.

The Mn for such polymers can be determined by several known techniques.A convenient method for such determination is by gel permeationchromatography (GPC) which additionally provides molecular weightdistribution information, see W. W. Yau, J. J. Kirkland and D. D. Bly,"Modern Size Exclusion Liquid Chromatography", John Wiley and Sons, NewYork, 1979.

The oil soluble polymeric hydrocarbon backbone may be functionalized toincorporate a functional group into the backbone of the polymer, or aspendant groups from the polymer backbone. The functional group typicallywill be polar and contain one or more hetero atoms such as P, 0, S, N,halogen, or boron. It can be attached to a saturated hydrocarbon part ofthe oil soluble polymeric hydrocarbon backbone via substitutionreactions or to an olefinic portion via addition or cycloadditionreactions. Alternatively, the functional group can be incorporated intothe polymer by oxidation or cleavage of a small portion of the end ofthe polymer (e.g., as in ozonolysis).

Useful functionalization reactions include. halogenation of the polymerat an olefinic bond and subsequent reaction of the halogenated polymerwith an ethylenically unsaturated functional compound. reaction of thepolymer with an unsaturated functional compound by the "ene" reactionabsent halogenation (an example of the former functionalization ismaleation where the polymer is reacted with maleic acid or anhydride);reaction of the polymer with at least one phenol group (this permitsderivatization in a Mannich Base-type condensation), reaction of thepolymer at a point of unsaturation with carbon monoxide using aKoch-type reaction to introduce a carbonyl group in an iso or neoposition, reaction of the polymer with the functionalizing compound byfree radical addition using a free radical catalyst, reaction with athiocarboxylic acid derivative; and reaction of the polymer by airoxidation methods, epoxidation, chioroamination, or ozonolysis.

The functionalized oil soluble polymeric hydrocarbon backbone is thenfurther derivatized with a nucleophilic amine, amino-alcohol, or mixturethereof to form oil soluble salts, amides, imides, amino-esters, andoxazolines. Useful amine compounds include those described herein afterin more detail in relation to the MFVM. Preferred amines are aliphaticsaturated amines. Non-limiting examples of suitable amine compoundsinclude. 1,2-diaminoethane; 1,3-diaminopropane; 1,4-diaminobutane;1,6-diaminohexane; polyethylene amines such as diethylene triamine;triethylene tetramine; tetraethylene pentamine; and polypropyleneaminessuch as 1,2-propylene diamine; and di-(1,2-propylene)triamine.

Useful amines also include polyoxyalkylene polyamines and the polyamidoand related amido-amines as disclosed in U.S. Pat, Nos. 4,857,217,4,956,107, 4,963,275 and 5229022. Also usable istris(hydroxymethyl)amino methane (THAM) as described in U.S. Pat. Nos.4,102,798, 4,113,639 and 4,116,876; and GB-A-989409. Dendrimers,star-like amines, and comb-structure amines may also be used. Similarly,one may use the condensed amines of U.S. Pat. No. 5,053,152. Thefunctionalized polymer of this invention is reacted with the aminecompound according to conventional techniques as in EP-A-208560 and U.S.Pat. No. 5,229,022 using any of a broad range of reaction ratios asdescribed therein.

A preferred group of nitrogen containing ashless dispersants includesthose derived from polyisobutylene substituted with succinic anhydridegroups and reacted with polyethylene amines (e.g. tetraethylenepentamine, pentaethylene, polyoxypropylene diamine) aminoalcohols suchas trismethylolaminomethane and optionally additional reactants such asalcohols and reactive metals e.g. pentaerythritol, and combinationsthereof).

Also useful as nitrogen containing ashless dispersants are dispersantswherein a polyamine is attached directly to the long chain aliphatichydrocarbon as shown in U.S. Pat, Nos. 3,275,554 and 3,565,804 where ahalogen group on a halogenated hydrocarbon is displaced with variousalkylene polyamines. Another class of nitrogen-containing ashlessdispersants comprises Mannich base condensation products. Such Mannichcondensation products may include a long chain, high molecular weighthydrocarbon (e.g., Mn of 1,500 or greater) on the benzene group or maybe reacted with a compound containing such a hydrocarbon, for example,polyalkenyl succinic anhydride as shown in U.S. Pat. No. 3,442,808.

Examples of dispersants prepared from polymers prepared from metallocenecatalysts and then functionalized, derivatized, or functionalized andderivatized are described in U.S. Pat. Nos. 5,266,223, 5,128,056,5,200,103, 5,225,092, 5,151,204 and 5,334,775; WO-A-94/13709 and94/19436; and EP-A440506, 513211 and 513157.

The functionalizations, derivatizations, and post-treatments describedin the following patents may also be adapted to functionalize and/orderivative the preferred polymers described above: U.S. Pat. Nos.3,275,554, 3,565,804, 3,442,808, 3,442,808, 3,087,936 and 3254025.

C. Viscosity Modifiers

The multifunctional viscosity modifier may be one or more of:polymethacrylates derivatised with nitrogen containing monomers such asvinylpyridine, N-vinylpyrrolidinone, or N,N'-dimethylaminoethylmethacrylate; ethylene-propylene copolymers directly amine derivatised,hydrogenated star polymers reacted with a carboxylic acid derivative andthen reacted with an amine; hydrogenated styrenebutadiene-ethylene oxideblock copolymers; and ethylene alphaolefin copolymers solution or meltgrafted with ethylenically unsaturated a dicarboxylic acid derivativeand then reacted with an amine. Typically multifunctional viscositymodifiers are derived from a polymer having a number average molecularweight (Mn) of greater than 7000, as distinct from ashless dispersants,as defined above.

In a preferred aspect the multifunctional viscosity modifier comprises aderivatized ethylene-alpha olefin copolymer comprising an adduct of

(i) a copolymer having a number average molecular weight of from 20,000to 100,000, functionalized with mono- or dicarboxylic acid material; and

(ii) at least one amine,

and in a particularly preferred aspect the ethylene-alpha olefincopolymer comprises either

a) from 30 to 60 weight percent monomer units derived from ethylene andfrom 70 to 40 weight percent monomer units derived from alpha-olefin, or

b) from 60 to 80 weight percent monomer units derived from ethylene andfrom 40 to 20 weight percent monomer units derived from alpha olefin.

A highly preferred class of multifunctional viscosity modifiers whichmay be used in the invention comprise a mixture of derivatisedethylene-alpha olefin copolymers A and B, both comprising an adduct of

(i) a copolymer having a number average molecular weight of from 20,000to 100,000, functionalized with mono- or dicarboxylic acid material; and

(ii) at least one amine, and wherein:

the ethylene-alpha olefin copolymer of derivatized copolymer A comprisesfrom 30 to 60 weight percent monomer units derived from ethylene andfrom 70 to 40 weight percent monomer units derived from alpha-olefin;and

the ethylene-alpha olefin copolymer of derivatized copolymer B comprisesfrom 60 to 80 weight percent monomer units derived from ethylene andfrom 40 to 20 weight percent monomer units derived from alpha olefin,

with the proviso that the respective weight percents of ethylene derivedmonomer units present in said derivatized copolymers A and B differ byat least 5 weight percent.

The multifunctional viscosity modifiers used in the present inventionmay be prepared by known techniques. The preferred mixture ofderivatized ethylene-alpha-olefin copolymers may be prepared byfunctionalising and derivatising ethylene alphaolefin copolymers such asdescribed in EP-A-616616 and WO-A-94/1 3763.

Ethylene Alpha-olefin Copolymers

The ethylene-alpha olefin copolymers comprise monomer units derived fromethylene and alpha-olefins which are typically C₃ to C₂₈, preferably C₃to C₁₈, most preferably C₃ to C₈ alpha olefins. While not essential,such polymers preferably have a degree of crystallinity of less than 25wt. percent as determined by x-ray and differential scanningcalorimetry. Copolymers of ethylene and propylene are most preferred.

Representative examples of other suitable alpha-olefins include1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene,etc; also branched chain alpha-olefins, such as 4 methyl-1-pentene,4-methyl-1-hexene, 5 methyl pentene-1, 4.4 dimethyl-1-pentene, and 6methylheptene-1 and mixtures thereof. Ter- and tetra- copolymers areincluded within the scope of "copolymers".

Ethylene alpha-olefin copolymers used in the invention preferably have anumber average molecular weight (Mn) of from 25,000 to 80,000 and mostpreferably from 25,000 to about 50,000. Suitable polymers will typicallyhave a narrow molecular weight distribution (MWD), as determined by theratio of weight average molecular weight (Mw) to number averagemolecular weight (Mn). Polymers having a Mw/Mn of less than 10,preferably less than 7, and more preferably 4 or less are mostdesirable. As used herein (Mn) and (Mw) may be measured by well knowntechniques such as vapor phase osmometry (VPO), membrane osmometry andgel permeation chromatography (GPC). The synthesis of polymers having asuitable molecular weight and narrow MWD may be obtained by techniquesknown in the art including choice of synthesis conditions and postsynthesis treatment such as extrusion at elevated temperature, highshear mastication under elevated temperatures in the presence ofperoxides or air. thermal degradation, and fractional precipitation fromsolution.

The copolymers employed to make the component blends of the presentinvention are differentiated primarily by their ethylene content.Derivatised copolymer A is derived from a low ethylene monomer unitcontent copolymer and derivatised copolymer B is derived from a highethylene monomer unit content copolymer. More specifically, the lowethylene content copolymer will comprise preferably from 40 to 50 andmost preferably from 42 to 46 (e.g., 44) weight percent monomer unitsderived from ethylene; and preferably from 60 to 50, and most preferablyfrom 58 to 54 (e.g., 56) weight percent monomer units derived fromalpha-olefin. The high ethylene content copolymer will comprisepreferably from 65 to 75, and most preferably from 68 to 73 (e.g., 70)weight percent monomer units derived from ethylene; and preferably from35 to 25, and most preferably from 32 to 27 (e.g., 30) weight percentmonomer units derived from alpha-olefin.

The above ethylene contents are subject to the proviso that the ethylenecontent of the high and low ethylene copolymers must differ by at least5, preferably at least and most preferably at least 15 weight percent.

For ease of discussion, derivatised copolymers derived from the lowethylene content copolymer, as described above, are referred to hereinas Component A, and derivatised copolymers derived from the highethylene content copolymer, as described above, are referred to hereinas Component B.

Many such ethylene alpha olefin copolymers are available as items ofcommerce and their composition and methods for producing them are wellknown in the art. Representative examples include: MDV-90-9 manufacturedby Exxon Chemical Company, an ethylene-propylene copolymer containing 70weight percent ethylene, which is further characterized by a Mooneyviscosity, ML, 1+4 @ 125° C. of 18; and VISTALON 457 manufactured by.Exxon Chemical Company, a 44 weight percent ethylene, ethylene-propylenecopolymer which is further characterized by a Mooney viscosity, ML 1+4 @125° C. of 28.

As indicated above, the MFVM used in present invention comprises a blendof Components A and B. Such blends will comprise typically weight ratios(referred to herein as "blend ratios") of A: B of from 2.3:1 to 0.18: 1,preferably from 1.2:1 to 0.25: 1, and most preferably from 0.8:1 to0.33:1. Such blend ratios are also applicable to unfunctionalized highand low ethylene content polymer blends in preparation forfunctionalization. To prepare the MFVM used in the present invention,the high and low ethylene alpha-olefin copolymers are firstfunctionalized and then derivatized.

Functionalized Polymers

By functionalized, it is meant that the polymer is chemically modifiedto have at least one functional group present within its structure,which functional group is capable of undergoing further chemicalreaction (e.g., derivatization) with other materials. The preferredfunctionalization reaction is accomplished by reaction of the polymerwith a compound containing the desired functional group by free radicaladdition using a free radical catalyst. More specifically, polymerfunctionalized with mono- or dicarboxylic acid material, i.e., acid,anhydride, salt or acid ester suitable for use in this invention,typically includes the reaction product of the polymer with amonounsaturated carboxylic reactant comprising at least one of (i)monounsaturated C₄ to C₁₀ dicarboxylic acids (preferably wherein (a) thecarboxyl groups are vicinyl, i.e., located on adjacent carbon atoms and(b) at least one, more preferably both, of said adjacent carbon atomsare part of said monounsaturation). (ii) derivatives of (i) such asanhydrides or C₁ to C₅ alcohol derived mono- or diesters of (i); (iii)monounsaturated C₃ to C₁₀ monocarboxylic acids wherein the carbon-carbondouble bond is conjugated allylic to the carboxyl group, i.e., of thestructure --C═C--CO--; and (iv) derivatives of (iii) such as C₁ to C₅alcohol derived monoesters of (iii).

Suitable unsaturated acid materials thereof which are useful functionalcompounds, include acrylic acid, crotonic acid, methacrylic acid, maleicacid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride,citraconic acid, citraconic anhydride, mesaconic acid, glutaconic acid,choromaleic acid, aconitic acid, crotonic acid, methylcrotonic acid,sorbic acid, 3-hexenoic acid, 10-decenoic acid,2-pentenel,3,5-tricarboxylic acid, cinnamic acid, and lower alkyl (e.g.,C₁ to C₄ alkyl) acid esters of the foregoing, e.g., methyl maleate,ethyl fumarate, methyl fumarate, etc. Particularly preferred are theunsaturated dicarboxylic acids and their derivatives, especially maleicacid, fumaric acid and maleic anhydride.

The two functionalised copolymers described above can be prepared inseveral ways. The functional groups can be grafted onto each of thecopolymers separately and then the functionalized copolymers can then bemechanically blended at the above described blend ratios. In thepreferred method for practicing the invention, the two copolymers aresimultaneously functionalized and blended at the same time by feedinginto an extruder, masticator or reactor.

The extrusion process is continuous, while the masticator process is abatch process. Both take place in a polymer melt, i.e., the polymer ismelted in the high temperature, high shear conditions of this equipment.The functionalization takes place substantially in absence of a solvent.The reactor process is a process similar to the masticator batch processbut the polymer is functionalized once it is dissolved in a solvent suchas mineral oil. The extruder and masticator processes can provideefficient peroxide and or thermo oxidative induced molecular weightreduction of the copolymers, should a lower molecular weight be desiredthan that of the copolymer that is available.

It will be understood that blends of the high and low ethylene contentpolymers will create a bimodal distribution of ethylene content notachievable by making a single polymer having a single average ethylenecontent.

Free-radical induced grafting can take place in a polymer melt in aextruder or masticator, or when using a conventional batch reactor withthe polymer dissolved in a solvent, preferably in a mineral lubricatingoil. The free-radical grafting is preferably carried out using freeradical initiators such as peroxides, hydroperoxides, and azo compoundsand preferably those which have a boiling point greater than about 100°C. and which decompose thermally within the grafting temperature rangeto provide said free radicals. The initiator is generally used at alevel of between about 0.005 percent and about 1 percent, based on thetotal weight of the polymer.

The ethylenically unsaturated carboxylic acid material, preferablymaleic anhydride, will be generally used in an amount ranging from 0.01percent to 10 percent, preferably 0.1 to 2.0 percent, based on weight ofcopolymer. The aforesaid carboxylic acid material and free radicalinitiator are generally used in a weight percent ratio range of 1.0:1 to30:1, preferably 3.0:1 to 6:1.

When the copolymer grafting takes place in a solvent in a reactor, theinitiator grafting is preferably carried out in an inert atmosphere,such as that obtained by nitrogen blanketing. While the grafting can becarried out in the presence of air, the yield of the desired graftpolymer is generally thereby decreased as compared to grafting under aninert atmosphere substantially free of oxygen. The grafting time willusually range from 0.1 to 12 hours, preferably from 0.5 to 6 hours, morepreferably 0.5 to 3 hours. In the grafting process, usually thecopolymer solution is first heated to grafting temperature andthereafter said unsaturated carboxylic acid material and initiator areadded with agitation, although they could have been added prior toheating. When the reaction is complete, the excess acid material can beeliminated by an inert gas purge, e.g., nitrogen sparging.

The grafting is preferably carried out in a mineral lubricating oilwhich need not be removed after the grafting step but can be used as thesolvent in the subsequent reaction of the graft polymer with the aminematerial and as a solvent for the end product to form the lubricatingadditive concentrate. The oil having attached, grafted carboxyl groups,when reacted with the amine material will also be converted to thecorresponding derivatives but such derivatives are of little use toimprovement in performance.

A description for functionalizing in a masticator can be found in U.S.Pat. No. 4,735,736, and a description for functionalizing thecopolymers, dissolved in a solvent such as mineral oil, in a reactor canbe found in U.S. Pat. No. 4,517,104, the disclosures of which are hereinincorporated by reference.

In contrast, reactions carried out in the polymer melt, particularly inan extruder, are characterized by maximized reaction rates and minimizedreactor volumes (due to the absence of a diluent solvent), by absence ofside reactions with the solvent and by minimized residence times (due tothe absence of dissolution and recovery steps before and after thereaction, respectively). Methods for extruder grafting are disclosed incommonly assigned U.S. Pat. No. 5,290,461, the disclosure of which isherein incorporated by reference.

In order to prevent or minimize the crosslinking or gellation of thegrafted copolymer, particularly when it is subsequently aminated withamines having more than one reactive primary or secondary nitrogens, anoptional acid functionalized low molecular weight hydrocarbyl componentcan be added to the functionalized polymers to moderate molecular weightgrowth of the derivatized polymer. Such materials are referred to hereinas "Growth Regulators". Suitable Growth Regulators include. hydrocarbylsubstituted succinic anhydride or acid having 12 to 49 carbons,preferably 16 to 49 carbons in said hydrocarbyl group, long chainmonocarboxylic acid of the formula RCOOH where R is a hydrocarbyl groupof 50 to 400 carbons and long chain hydrocarbyl substituted succinicanhydride or acid having 50 to 400 carbons in said hydrocarbyl group.Primarily because of its ready availability and low cost, thehydrocarbyl portion, e.g., alkenyl groups, of the carboxylic acid oranhydride is preferably derived from a polymer of a C₂ to C₅ monoolefin,said polymer generally having a molecular weight of about 140 to 6500,e.g., 700 to about 5000, most preferably 700 to 3000 molecular weight.Particularly preferred is polyisobutylene of 950 molecular weight.

Derivatized Polymers

A derivatized polymer is one which has been chemically modified toperform one or more functions in a significantly improved way relativeto the unfunctionalized polymer and or the functionalized polymer. Theprimary new function sought to be imparted to the functionalizedpolymers of the present invention is dispersancy in lubricating oilcompositions. Thus, the derivatized polymers used in the invention arethe reaction products of the above recited functionalized polymers withamines.

Of the various amines useful in the practice of this invention, oneamine type has two or more primary amine groups, wherein the primaryamine groups may be unreacted, or wherein one of the amine groups mayalready be reacted. Particularly preferred amine compounds includealkylene polyamines, polyoxyalkylene polyamines, preferably wherein thealkylene groups are straight or branched chains containing from 2 to 7,and more preferably 2 to 4 carbon atoms.

Examples of the alkylene polyamines include methylene amines, ethyleneamines, butylene amines, propylene amines, pentylene amines, hexyleneamines, heptylene amines, octylene amines, other polymethylene amines,the cyclic and higher homologs of these amines such as the piperazines,the amino-alkyl-substituted piperazines, etc. These amines include, forexample, ethylene diamine, diethylene triamine, triethylene tetramine,propylene diamine, di(heptamethylene)triamine, tripropylene tetramine,tetraethylene pentamine, trimethylene diamine, pentaethylene hexamine,di(trimethylene)triamine, 2-heptyl-3-(2-aminopropyl)imidazoline,4-methylimidazoline, 1,3-bis-(2-aminoethyl)imidazoline, pyrimidine,1-(2-aminopropyl)-piperazine, 1,4-bis-(2-aminoethyl)piperazine,N,N-dimethyaminopropyl amine, N,N-dioctylethyl amine,N-octyl-N'-methylethylene diamine, 2-methyl-1-(2-aminobutyl) piperazine,etc. The ethylene amines which are particularly useful are described,for example, in the Encyclopaedia of Chemical Technology under theheading of "Ethylene Amines" (Kirk and Othmer), Volume 5, pgs. 898-905.Interscience Publishers, New York (1950).

The polyoxyalkylene polyamines are preferably polyoxyalkylene diaminesand polyoxyalkylene triamines, and may typically have average molecularweights ranging from 200 to 4000 and preferably from 400 to 2000. Thepreferred polyoxyalkylene polyamines include the polyoxyethylene andpolyoxypropylene diamines and the polyoxypropylene triamines havingaverage molecular weights ranging from 200 to 2000. The polyoxyalkylenepolyamines are commercially available and may be obtained, for example,from the Jefferson Chemical Company, Inc. under the trade name"Jeffamines D-230, D-400, D-1000, D-2000, T-403", etc.

Primary amines are more preferred because of the stability of the imideproducts formed. Most preferred are primary amines, RNH₂, in which the Rgroup contains functionalities that it is desired to have in the finalproduct. Although such products contain two functionalities, the imidefunctionality formed by reaction of the primary amine is relativelyinert and serves as a stable linkage between the functionality in the Rgroup and the polymer backbone. In this invention it is desired that theR group of the primary amine RNH₂ contain tertiary amine functionality.

Examples of useful primary amines, RNH₂, in which the R group containstertiary amine functionality include: N,N-dimethylethylenediamine,N,N-diethylethylenediamine, N, N-dimethyl-1,3-propanediamine,N,N-diethyl-1,3-propanediamine, 4-aminomorpholine,4-(aminomethyl)pyridine, 4-(2-aminoethyl)morpholine and4-(3-aminopropyl)morpholine. Preferred reactive compounds for reactionwith grafted maleic anhydride in the practice of this invention are4-(3-aminopropyl)morpholine and 1-(2-aminoethyl)- piperazine.

Still other amines useful in the practice of this invention includeamino-aromatic polyamine compounds such as N-arylphenylenediamines.Particularly preferred N-arylphenylenediamines are theN-phenylphenylenediamines, for example, N-phenyl-1,4-phenyienediamine,N-phenyl-1,3-phenylenediamine, N-phenyl-1,2-phenylenediamine,N-naphthyl-phenylenediamine, N-phenyl-naphthalenediamine andN'-aminopropyl-N-phenylphenylene- diamine.

Other useful amines include aminothiazoles such as aminothiazole,aminobenzothiazole, aminobenzothiadiazole and aminoalkylthiazole,aminopyrroles, phenothiazines and phenothiazine derivatives,particularly 10-aminopropyl-phenothiazine,amino-3-propylaminophenothiazine, N-amino-propyl-2-naphthylamine andN-aminopropyidiphenylamine.

Mixtures of amines, particularly mixtures of two or more of the abovecompounds, may be used.

As indicated above, functionalization can be conducted separately on thehigh and low ethylene content polymers or the high and low ethylenecontent polymers can be blended at the aforedescribed blend ratios andthen functionalized. If the latter option is employed, derivatization isconducted on the blend. If separate functionalization is employed, onehas the additional options of derivatizing separately and blending thefinal derivatized products or blending the separately functionalizedcopolymers and derivatizing the blend simultaneously.

The functionalized ethylene alpha-olefin copolymers can be derivatizedwith amine in the melt or in solution. Melt derivatizations can in turnbe conducted in an extruder or masticator, when conditions aresubstantially the same as the functionalization step. A stripping stepcan take place prior to amination to remove the unwanted by-products ofthe graft step which can lead to undesirable by-products as aconsequence of the amination. When the amination takes place in areactor, the functionalized polymer is dissolved in solution (e.g., inoil) at an amount of typically from 5 to 30, preferably 10 to 20, wt.percent polymer, based on the solution weight. Accordingly, thefunctionalized polymer is preheated at a temperature of from about 100°C. to 250° C., preferably from 170° to 230° C., said amine and optionalgrowth regulator added and temperatures maintained for from 1 to 10hours, usually 2 to 6 hours.

It has been found that many of these multifunctional viscosity modifierswhich contain unreacted primary or secondary amine, can undergo anincrease in molecular weight which is manifested by product gellation orviscosity growth of the resultant concentrates in oil. For this reasonit has been found useful to post-treat or cap these products with anacid such as a C₁₂ to C₁₆ hydrocarbyl substituted dicarboxylic acid oranhydride to stabilize the molecular weight.

The lubricating oils of the invention typically contain a minor amount,e.g. 0.001 up to 50 mass percent, preferably 0.005 to 25 mass percent,based on the weight of the lubricating oil, of the derivatizedcopolymers as MFVM. The viscosity modifier system used in the inventionwill be used in an amount to give the required viscositycharacteristics. When used in lubricating oils for automotive or dieselcrankcase lubrication the MFVM is present at concentrations usuallywithin the range of from 0.01 to 10 mass percent, e.g., 0.1 to 6.0 masspercent, preferably 0.25 to 3.0 mass percent (measured as polymer), ofthe total composition.

A single multifunctional viscosity modifier may be used alone, or it maybe used in combination with additional conventional viscosity modifiers,either monofunctional or multifunctional.

Additional additives are typically incorporated into the compositions ofthe present invention. Examples of such additives are ashlessdispersants, metal or ash containing detergents, antioxidants, anti-wearagents, friction modifiers, rust inhibitors, anti-foaming agents,demulsifiers, and pour point depressants.

D. Detergent

Metal-containing or ash-forming detergents function both as detergentsto reduce or remove deposits and as acid neutralizers or rustinhibitors, thereby reducing wear and corrosion and extending enginelife. Detergents generally comprise a polar head with a long hydrophobictail, with the polar head comprising a metal salt of an acidic organiccompound. The salts may contain a substantially stoichiometric amount ofthe metal in which case they are usually described as normal or neutralsalts, and would typically have a total base number or TBN (as may bemeasured by ASTM D2896) of from 0 to 80. It is possible to include largeamounts of a metal base by reacting an excess of a metal compound suchas an oxide or hydroxide with an acidic gas such as carbon dioxide. Theresulting overbased detergent comprises neutralised detergent as theouter layer of a metal base (e.g. carbonate) micelle. Such overbaseddetergents may have a TBN of 150 or greater, and typically of from 250to 450 or more.

Detergents that may be used include oil-soluble neutral and overbasedsulfonates, phenates, sulfurized phenates, thiophosphonates,salicylates, and naphthenates and other oil-soluble carboxylates of ametal, particularly the alkali or alkaline earth metals, e.g., sodium,potassium, lithium, calcium, and magnesium. The most commonly usedmetals are calcium and magnesium, which may both be present indetergents used in a lubricant, and mixtures of calcium and/or magnesiumwith sodium. Particularly convenient metal detergents are neutral andoverbased calcium sulfonates having TBN of from 20 to 450 TBN, andneutral and overbased calcium phenates and sulfurized phenates havingTBN of from 50 to 450.

Sulfonates may be prepared from sulfonic acids which are typicallyobtained by the sulfonation of alkyl substituted aromatic hydrocarbonssuch as those obtained from the fractionation of petroleum or by thealkylation of aromatic hydrocarbons. Examples included those obtained byalkylating benzene, toluene, xylene, naphthalene, diphenyl or theirhalogen derivatives such as chlorobenzene, chlorotoluene andchloronaphthalene. The alkylation may be carried out in the presence ofa catalyst with alkylating agents having from about 3 to more than 70carbon atoms. The alkaryl sulfonates usually contain from about 9 toabout 80 or more carbon atoms, preferably from about 16 to about 60carbon atoms per alkyl substituted aromatic moiety.

The oil soluble sulfonates or alkaryl sulfonic acids may be neutralizedwith oxides, hydroxides, alkoxides, carbonates, carboxylate, sulfides,hydrosulfides, nitrates, borates and ethers of the metal. The amount ofmetal compound is chosen having regard to the desired TBN of the finalproduct but typically ranges from about 100 to 220 mass % (preferably atleast 125 mass %) of that stoichiometrically required.

Metal salts of phenols and sulfurised phenols are prepared by reactionwith an appropriate metal compound such as an oxide or hydroxide andneutral or overbased products may be obtained by methods well known inthe art. Sulfurised phenols may be prepared by reacting a phenol withsulfur or a sulfur containing compound such as hydrogen sulfide, sulfurmonohalide or sulfur dihalide, to form products which are generallymixtures of compounds in which 2 or more phenols are bridged by sulfurcontaining bridges.

E. Antiwear and Antioxidant Agent

Dihydrocarbyl dithiophosphate metal salts are frequently used asanti-wear and antioxidant agents. The metal may be an alkali or alkalineearth metal, or aluminum, lead, tin, molybdenum, manganese, nickel orcopper. The zinc salts are most commonly used in lubricating oil inamounts of 0.1 to 10, preferably 0.2 to 2 mass %, based upon the totalweight of the lubricating oil composition. They may be prepared inaccordance with known techniques by first forming a dihydrocarbyldithiophosphoric acid (DDPA), usually by reaction of one or more alcoholor a phenol with P₂ S₅ and then neutralizing the formed DDPA with a zinccompound. For example, a dithiophosphoric acid may be made by reactingmixtures of primary and secondary alcohols. Alternatively, multipledithiophosphoric acids can be prepared where the hydrocarbyl groups onone are entirely secondary in character and the hydrocarbyl groups onthe others are entirely primary in character. To make the zinc salt anybasic or neutral zinc compound could be used but the oxides, hydroxidesand carbonates are most generally employed. Commercial additivesfrequently contain an excess of zinc due to use of an excess of thebasic zinc compound in the neutralization reaction.

The preferred zinc dihydrocarbyl dithiophosphates are oil soluble saltsof dihydrocarbyl dithiophosphoric acids and may be represented by thefollowing formula. ##STR1## wherein R and R' may be the same ordifferent hydrocarbyl radicals containing from 1 to 18, preferably 2 to12, carbon atoms and including radicals such as alkyl, alkenyl, aryl,arylalkyl, alkaryl and cycloaliphatic radicals. Particularly preferredas R and R' groups are alkyl groups of 2 to 8 carbon atoms. Thus, theradicals may, for example, be ethyl, n-propyl, i-propyl, n-butyl,i-butyl, sec-butyl, amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl,octadecyl, 2-ethylhexyl, phenyl, butylphenyl, cyclohexyl,methylcyclopentyl, propenyl, butenyl. In order to obtain oil solubility,the total number of carbon atoms (i.e. R and R') in the dithiophosphoricacid will generally be about 5 or greater. The zinc dihydrocarbyldithiophosphate can therefore comprise zinc dialkyl dithiophosphates.Conveniently at least 50 (mole) % of the alcohols used to introducehydrocarbyl groups into the dithiophosphoric acids are secondaryalcohols.

Oxidation inhibitors or antioxidants reduce the tendency of mineral oilsto deteriorate in service which deterioration can be evidenced by theproducts of oxidation such as sludge and varnish-like deposits on themetal surfaces and by viscosity growth. Such oxidation inhibitorsinclude hindered phenols, alkaline earth metal salts ofalkylphenolthioesters having preferably C₅ to C₁₂ alkyl side chains,calcium nonylphenol sulfide, ashless oil soluble phenates and sulfurizedphenates, phosphosulfurized or sulfurized hydrocarbons, phosphorousesters, metal thiocarbamates, oil soluble copper compounds as describedin U.S. Pat. No. 4,867,890, and molybdenum containing compounds.

Typical oil soluble aromatic amines having at least two aromatic groupsattached directly to one amine nitrogen contain from 6 to 16 carbonatoms. The amines may contain more than two aromatic groups. Compoundshaving a total of at least three aromatic groups in which two aromaticgroups are linked by a covalent bond or by an atom or group (e.g., anoxygen or sulfur atom, or a --CO--, --SO₂ -- or alkylene group) and twoare directly attached to one amine nitrogen also considered aromaticamines. The aromatic rings are typically substituted by one or moresubstituents selected from alkyl, cycloalkyl, alkoxy, aryloxy, acyl,acylamino, hydroxy, and nitro groups.

OTHER ADDITIVES

Friction modifiers may be included to improve fuel economy. Oil-solublealkoxylated mono- and diamines are well known to improve boundary layerlubrication. The amines may be used as such or in the form of an adductor reaction product with a boron compound such as a boric oxide, boronhalide, metaborate, boric acid or a mono-, di- or trialkyl borate.

Other friction modifiers include esters formed by reacting carboxylicacids and anhydrides with alkanols. Other conventional frictionmodifiers generally consist of a polar terminal group (e.g. carboxyl orhydroxyl) covalently bonded to an oleophillic hydrocarbon chain. Estersof carboxylic acids and anhydrides with alkanols are described in U.S.Pat. No. 4,702,850. Examples of other conventional friction modifiersare described by M. Belzer in the "Journal of Tribology" (1992), Vol. 114, pp. 675-682 and M. Belzer and S. Jahanmir in "Lubrication Science"(1988), Vol. 1, pp. 3-26.

Rust inhibitors selected from the group consisting of nonionicpolyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, andanionic alkyl sulfonic acids may be used.

Copper and lead bearing corrosion inhibitors may be used, but aretypically not required with the formulation of the present invention.Typically such compounds are the thiadiazoie polysuifides containingfrom 5 to 50 carbon atoms, their derivatives and polymers thereof.Derivatives of 1,3,4 thiadiazoies such as those described in U.S. Pat.Nos. 2,719,125; 2,719,126, and 3,087,932, are typical. Other similarmaterials are described in U.S. Pat. Nos. 3,821,236; 3,904,537;4,097,387; 4,107,059; 4,136,043. 4,188,299. and 4,193,882. Otheradditives are the thio and polythio sulfenamides of thiadiazoies such asthose described in UK. Patent Specification No. 1,560,830.Benzotriazoies derivatives also fall within this class of additives.When these compounds are included in the lubricating composition, theyare preferably present in an amount not exceeding 0.2 mass % activeingredient.

A small amount of a demulsifying component may be used. A preferreddemulsifying component is described in EP 330,522. It is obtained byreacting an alkylene oxide with an adduct obtained by reacting abis-epoxide with a polyhydric alcohol. The demulsifier should be used ata level not exceeding 0.1 mass % active ingredient. A treat rate of0.001 to 0.05 mass % active ingredient is convenient.

Pour point depressants, otherwise known as lube oil flow improvers,lower the minimum temperature at which the fluid will flow or can bepoured. Such additives are well known. Typical of those additives whichimprove the low temperature fluidity of the fluid are C₈ to C₁₈ dialkylfumarate/vinyl acetate copolymers and polyalkylmethacrylates.

Foam control can be provided by many compounds including an antifoamantof the polysiloxane type, for example, silicone oil or polydimethylsiloxane.

Lubricating compositions may also contain elastomer comparability aidsfor elastomeric seals such as Viton or fluorocarbon seals and nitrileseals. Carboxylic acids and unsaturated hydrocarbons have been used forsuch a purpose.

Some of the above-mentioned additives can provide a multiplicity ofeffects; thus for example, a single additive may act as adispersant-oxidation inhibitor. This approach is well known and does notrequire further elaboration.

When lubricating compositions contain one or more of the above-mentionedadditives, each additive is typically blended into the base oil in anamount which enables the additive to provide its desired function.Representative effective amounts of such additives, when used incrankcase lubricants, are listed below. All the values listed are statedas mass percent active ingredient.

    ______________________________________                         Mass %  Mass %    Additive             (Broad) (Preferred)    ______________________________________    Ashless Dispersant   0.1-3   1-3    Metal Detergents     0.1-15  0.2-9    Corrosion Inhibitor  0-5     0-1.5    Metal Dihydrocarbyl Dithiophosphate                         0.1-6   0.1-4    Anti-oxidant         0-5     0.01-2    Pour Point Depressant                         0.01-5  0.01-1.5    Anti-Foaming Agent   0-5     0.001-0.15    Supplemental Anti-wear Agents                         0-0.5   0-0.2    Friction Modifier    0-5     0-1.5    Viscosity Modifier   0.01-10 0.25-3    Low Saturate Base Oil                         Balance Balance    ______________________________________

In a preferred embodiment of the invention the oil comprises not morethan 2 mass % of ashless dispersant and preferably does not containmonofunctional viscosity modifier.

The components may be incorporated into a base oil in any convenientway. Thus, each of the components can be added directly to the oil bydispersing or dissolving it in the oil at the desired level ofconcentration. Such blending may occur at ambient temperature or at anelevated temperature.

Preferably all the additives except for the viscosity modifier and thepour point depressant are blended into a concentrate or additive packagedescribed herein as the detergent inhibitor package, that issubsequently blended into basestock to make finished lubricant. Use ofsuch concentrates is conventional. The concentrate will typically beformulated to contain the additive(s) in proper amounts to provide thedesired concentration in the final formulation when the concentrate iscombined with a predetermined amount of base lubricant.

Preferably the detergent inhibitor package is made in accordance withthe method described in U.S. Pat. No. 4,938,880. That patent describesmaking a premix of ashless dispersant and metal detergents that ispre-blended at a temperature of at least about 1000° C. Thereafter thepre-mix is cooled to at least 85° C. and the additional components areadded.

The final formulations may employ from 2 to 18 mass % and preferably 4to 15 mass % of the concentrate or additive package (including anydiluent or solvent contained in individual additives) with the remainderbeing viscosity modifier (in an appropriate amount to give the desiredviscometrics) and base oil.

The invention will now be described by of illustration only withreference to the following examples.

EXAMPLE 1

An SAE 15W-40 oil of the invention prepared from a basestock of 64 mass% saturates was tested in the Sequence VE engine test, using a detergentinhibitor package with a reduced amount of ashless dispersant such thatthe level of active ingredient of the ashless dispersant isapproximately 1.75 mass %. At a treat rate of 9.5 mass % of thepreferred multifunctional viscosity modifier as described inWO-A-94/13763, without any monofunctional viscosity modifier a passingengine test result was obtained. Details of the oil and test result areset out in the Table below.

    ______________________________________    Example              1    ______________________________________    Basestock (mass %)   56.5% BP 150ME                         24.0% BP 500ME                         Total saturates 64%    Viscosity Modifier (mass %)                         9.5% PARATONE 8500.sup.1    Additive Package (mass %)                         10.0% additive package.sup.2    Sequence VE Engine Test Results    Sludge Rating (pass = 9.0 for API SH                         9.1    quality level)    Varnish Rating (pass = 5.0 for API SH                         6.0    quality level)    Cam Lobe Wear (pass = 5.0 for API SH                         3.1    quality level)    ______________________________________     Footnotes:     .sup.1 multifunctional viscosity modifier according to WOA-94/13763     commercially available from Exxon Chemical Company and comprising an oil     solution of a blend of derivatised polymers, with a polymer content of     10.2 mass %;     .sup.2 a detergent inhibitor package comprising ashless dispersant,     metalcontaining detergents, antioxidant, antiwear additive, antifoam     additive, demulsifier, friction modifier and seal comparability aid.

We claim:
 1. A multigrade lubricating oil for an internal combustionengine having low and high temperature viscosity requirements whichcomprises:a. a basestock of lubricating oil viscosity having at least 20mass % of aromatics and less than 75 mass % of saturated hydrocarbons;b. less than 3 mass % of ashless dispersant derived from a polymer ofnumber average molecular weight (M) of not greater than 5000; and c.viscosity modifier to give the low and high temperature viscosityrequirements, which comprises at least one multifunctional viscositymodifier.
 2. An oil as claimed in claim 1, in which the overallsaturates level of the basestock is less than 70 mass %.
 3. An oil asclaimed in claim 1, in which the overall saturates level of thebasestock is less than 65 mass %.
 4. An oil as claimed in claim 1, inwhich the multifunctional viscosity modifier comprises a derivatizedethylene-alpha olefin copolymer comprising an adduct of(i) a copolymerhaving a number average molecular weight of from 20,000 to 100,000,functionalized with mono- or dicarboxylic acid material; and (ii) atleast one amine.
 5. An oil as claimed in claim 4, in which the ethylene-alpha olefin copolymer comprises eithera) from 30 to 60 mass %monomer units derived from ethylene and from 70 to 40 mass % monomerunits derived from alpha-olefin, or b) from 60 to 80 mass % monomerunits derived from ethylene and from 40 to 20 mass % monomer unitsderived from alpha olefin.
 6. An oil as claimed in claim 1, in which themultifunctional viscosity modifier comprises a mixture of derivatisedethylene-alpha olefin copolymers A and B, both comprising an adductof(i) a copolymer having a number average molecular weight of from20,000 to 100,000, functionalized with mono- or dicarboxylic acidmaterial; and (ii) at least one amine, and wherein:the ethylene-alphaolefin copolymer of derivatized copolymer A comprises from 30 to 60 mass% monomer units derived from ethylene and from 70 to 40 mass % monomerunits derived from alpha-olefin; and the ethylene-alpha olefin copolymerof derivatized copolymer B comprises from 60 to 80 mass % monomer unitsderived from ethylene and from 40 to 20 weight percent monomer unitsderived from alpha-olefin, with the proviso that the respective weightpercents of ethylene derived monomer units present in said derivatizedcopolymers A and B differ by at least 5 mass %.
 7. An oil as claimed inclaim 1, which is substantially free of monofunctional viscositymodifier and comprises an ashless dispersant in an amount not greaterthan 2 mass % (on the basis of active ingredient).
 8. A method forreducing or inhibiting varnish deposits in an internal combustion enginecomprising lubricating the internal combustion engine with a multigradelubricating oil which comprises a basestock of lubricating oil viscosityhaving at least 20 mass % of aromatics and less than 75 mass % ofsaturated hydrocarbons, less than 3 mass % of ashless dispersant derivedfrom a polymer of number average molecular weight (Mn) of not greaterthan 5000, and a viscosity modifier to meet low and high temperatureviscosity requirements for said multigrade lubricating oil whichcomprises at least one multifunctional viscosity modifier.
 9. A methodaccording to claim 8 wherein the overall saturates level of thebasestock is less than 70 mass %.
 10. A method according to claim 8wherein the overall saturates level of the basestock is less than 65mass %.
 11. A method according to claim 8 wherein the multifunctionalviscosity modifier comprises a derivatized ethylene-alpha olefincopolymer comprising an adduct of(i) a copolymer having a number averagemolecular weight of from 20,000 to 100,000, functionalized with mono- ordicarboxylic acid material; and (ii) at least one amine.
 12. A methodaccording to claim 11 wherein the ethylene-alpha olefin copolymercomprises eithera) from 30 to 60 mass % monomer units derived fromethylene and from 70 to 40 mass % monomer units derived fromalpha-olefin, or b) from 60 to 80 mass % monomer units derived fromethylene and from 40 to 20 mass % monomer units derived from alphaolefin.
 13. A method according to claim 8 wherein the multifunctionalviscosity modifier comprises a mixture of derivatised ethylene-alphaolefin copolymers A and B, both comprising an adduct of(i) a copolymerhaving a number average molecular weight of from 20,000 to 100,000,functionalized with mono- or dicarboxylic acid material; and (ii) atleast one amine, and wherein:the ethylene-alpha olefin copolymer ofderivatized copolymer A comprises from 30 to 60 mass % monomer unitsderived from ethylene and from 70 to 40 mass % monomer units derivedfrom alpha-olefin; and the ethylene-alpha olefin copolymer ofderivatized copolymer B comprises from 60 to 80 mass % monomer unitsderived from ethylene and from 40 to 20 weight percent monomer unitsderived from alpha-olefin, with the proviso that the respective weightpercents of ethylene derived monomer units present in said derivatizedcopolymers A and B differ by at least 5 mass %.
 14. A method accordingto claim 8 in which the multigrade lubricating oil is substantially freeof monofunctional viscosity modifier and comprises an ashless dispersantin an amount not greater than 2 mass % (on the basis of activeingredient).